Story highlights

Clayton Lockett and Charles Warner are now scheduled to be executed Tuesday

Defense attorney says there's no way to know if executions will be "humane"

States scrambled for new drugs after European manufacturers announced ban last year

Clayton Lockett and Charles Warner's executions are back on the schedule for next week after Oklahoma's high court lifted their stays, saying they had no right to know the source of the drugs that will be used to kill them.

The inmates, who are being held at the Oklahoma State Penitentiary in McAlester, where they are slated to be executed by lethal injection Tuesday, had challenged the state's so-called secrecy provision, which forbids disclosing the identities of anyone involved in the execution process or suppliers of any drugs or medical equipment.

Lockett and Warner also challenged the state Department of Corrections' failure to divulge which drugs would be used, but the department disclosed what drugs it intended to use before the high court's decision: midazolam, which causes unconsciousness, along with pancuronium bromide and potassium chloride, which shut down breathing and the heart.

The Oklahoma Supreme Court said the only remaining issue, then, is whether the state's failure to disclose its source for the drugs prevents the prisoners from challenging their executions using the Eighth Amendment's prohibition on cruel and unusual punishment. The court decided it did not.

"This court holds that the secrecy provision ... does not violate the inmates' constitutional right of access to the courts," the Wednesday ruling said.

Attorney Seth Day, who represents both men, called the ruling unacceptable and told CNN affiliate KFOR that there was no way to know if the prisoners' executions "would be carried out in a constitutional and humane manner."

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"It's not even known whether the lethal injection drugs to be used were obtained legally, and nothing is known about their source, purity, or efficacy, among other questions," he told the station. "Oklahoma's extreme secrecy surrounding lethal injection undermines our courts and democracy."

Attorney General Scott Pruitt applauded the decision, saying the state had a longstanding precedent of keeping the drug sources secret to avoid "schemes and intimidation used by defense counsel and other anti-death-penalty groups."

"These death row inmates have not contested their guilt for murdering two innocent victims nor have they contested their sentences of death. The legal wrangling of the attorneys for Lockett and Warner has served only to delay their punishment for the heinous crimes they committed," he told KFOR.

Lockett was convicted in 2000 of a bevy of crimes, including first-degree murder, first-degree rape, kidnapping and robbery in a 1999 home invasion and crime spree that left Stephanie Nieman dead and two people injured. In 2003, Warner was convicted for the 1997 first-degree rape and murder of his then-girlfriend's 11-month-old daughter, Adrianna Waller.

The constitutionality of lethal injection drugs and drug cocktails has made headlines since last year, when European manufacturers -- including Denmark-based Lundbeck, which manufactures pentobarbital -- banned U.S. prisons from using their drugs in executions. Thirty-two states were left to find new drug protocols.

"The states are scrambling to find the drugs," Richard Dieter, executive director of the Washington-based Death Penalty Information Center, said in November. "They want to carry out these executions that they have scheduled, but they don't have the drugs and they're changing and trying new procedures never used before in the history of executions."

If Lockett and Warner are executed next week, they would be the 194th and 195th inmates Oklahoma has executed since 1915.